Eight intact LTR retrotransposons （Nbr1-Nbr8） have been previously characterized from the genome of Nosema bombycis, a eu- karyotic parasite with a compact and reduced genome. Here we describe six novel transcribed ...Eight intact LTR retrotransposons （Nbr1-Nbr8） have been previously characterized from the genome of Nosema bombycis, a eu- karyotic parasite with a compact and reduced genome. Here we describe six novel transcribed Nbr elements （Nbr9-Nbr14） identified through either cDNA library or RT-PCR. Like previously determined ones, all of them belong to the Ty3/Gypsy superfamily. Retrotransposon diversity and incomplete domains with insertions （Nbr12）, deletions （Nbrll） and in-frame stop codons in coding regions （Nbr9） were detected, suggesting that both defective and loss events of LTR retrotransposon have happened in N. bornbycis genome. Analysis of selection showed that strong purifying selection acts on all elements except Nbr11. This implies that selective pressure keeps both these Nbrs and their functions in genome. Interestingly, Nbrll is under positive selection and some positively selected codons were identified, indicating that new functionality might have evolved in the Nbrll retrotransposon. Unlike other transposable elements, Nbrll has integrated into a conserved syntenic block and probably resulted in the inversion of both flanking regions. This demonstrates that transposable element is an important factor for the reshuffling and evolution of their host genomes, and may be maintained under natural selection.展开更多
Invasive species are characterized by the rapid growth and spread of their populations after establishing a foothold in new habitats, and there are now many examples of such species negatively affecting biodiversity a...Invasive species are characterized by the rapid growth and spread of their populations after establishing a foothold in new habitats, and there are now many examples of such species negatively affecting biodiversity and the economy. It is unclear why some species can become successful invaders, whereas most （even if closely related） remain noninvasive. We previously proposed a hypothesis that parasites associated with invading species can promote their invasive success if they are harmless toward the invaders but harmful to their competitors and/or predators in the newly colonized habitat. Here we discuss whether microsporidia that have recently been discovered in the invasive ladybird Harmonia axyridis contribute to its invasive success. We show that all H. axyridis beetles sourced from diverse collection sites all over the world carry abundant microsporidia. This suggests that both native and invasive H. axyridis populations are associated with these tolerated parasites, which were likely to have existed in native populations before expansion rather than being acquired in newly colonized areas. We describe the pathogenesis of the microsporidia during different developmental stages of H. axyridis and we address the possibility that the predation of its infected eggs and larvae by competing native ladybird species may lead to their infection and ultimately to their decline. Finally, we discuss our initial hypothesis： microsporidia that are tolerated by an invasive vector insect can be active against susceptible native competitors and/or predator species.展开更多
基金supported by the National Basic Research Program of China(No.2005CB121000)the project of Chongqing Science & Technology Commission(CSTC,No.2006AA5019 and 2009BB1241)+1 种基金the Programme of Introducing Talents of Discipline to Universities(No.B07045)State Development Fund at Risk of Callus Silk(No.M012005-000Y-00070)
文摘Eight intact LTR retrotransposons （Nbr1-Nbr8） have been previously characterized from the genome of Nosema bombycis, a eu- karyotic parasite with a compact and reduced genome. Here we describe six novel transcribed Nbr elements （Nbr9-Nbr14） identified through either cDNA library or RT-PCR. Like previously determined ones, all of them belong to the Ty3/Gypsy superfamily. Retrotransposon diversity and incomplete domains with insertions （Nbr12）, deletions （Nbrll） and in-frame stop codons in coding regions （Nbr9） were detected, suggesting that both defective and loss events of LTR retrotransposon have happened in N. bornbycis genome. Analysis of selection showed that strong purifying selection acts on all elements except Nbr11. This implies that selective pressure keeps both these Nbrs and their functions in genome. Interestingly, Nbrll is under positive selection and some positively selected codons were identified, indicating that new functionality might have evolved in the Nbrll retrotransposon. Unlike other transposable elements, Nbrll has integrated into a conserved syntenic block and probably resulted in the inversion of both flanking regions. This demonstrates that transposable element is an important factor for the reshuffling and evolution of their host genomes, and may be maintained under natural selection.
基金科技部“973”重点项目(2005CB121000)重庆市科技攻关计划项目(CSTC.2006AA5019)Supported by the Major Project of Chinese National Programs for Fundamental Research and Development (2005CB121003)~~
文摘Invasive species are characterized by the rapid growth and spread of their populations after establishing a foothold in new habitats, and there are now many examples of such species negatively affecting biodiversity and the economy. It is unclear why some species can become successful invaders, whereas most （even if closely related） remain noninvasive. We previously proposed a hypothesis that parasites associated with invading species can promote their invasive success if they are harmless toward the invaders but harmful to their competitors and/or predators in the newly colonized habitat. Here we discuss whether microsporidia that have recently been discovered in the invasive ladybird Harmonia axyridis contribute to its invasive success. We show that all H. axyridis beetles sourced from diverse collection sites all over the world carry abundant microsporidia. This suggests that both native and invasive H. axyridis populations are associated with these tolerated parasites, which were likely to have existed in native populations before expansion rather than being acquired in newly colonized areas. We describe the pathogenesis of the microsporidia during different developmental stages of H. axyridis and we address the possibility that the predation of its infected eggs and larvae by competing native ladybird species may lead to their infection and ultimately to their decline. Finally, we discuss our initial hypothesis： microsporidia that are tolerated by an invasive vector insect can be active against susceptible native competitors and/or predator species.
